Depression is a maximum cause of life's disability due to a disease, and is a disease considered to be important as a factor of suicide (non-patent documents 1 and 2). Antidepressants are largely divided into tricyclics, tetracyclics, triazolopyridines, SSRI (Selective Serotonin Reuptake Inhibitor), and SNRI (Serotonin Noradrenalin Reuptake Inhibitor). These antidepressants have a reuptake inhibitory action on noradrenaline or serotonin or a certain level of dopamine. However, a treatment effect by these drugs is limitative.
N-acetyl-D-mannosamine, which is an isomer of N-acetyl-D-glucosamine, is known as, for example, a starting material for enzymatic synthesis of sialic acid (N-acetylneuraminic acid) to be a pharmaceutical product and a starting material of a medicament. Since a sialic acid derivative can be enzymatically synthesized from a derivative of N-acetyl-D-mannosamine, N-acetyl-D-mannosamine is an industrially important substance. As a production method of N-acetyl-D-mannosamine, a method including addition of boric acid or borate during isomerization of N-acetylglucosamine under alkaline conditions, thereby increasing a mole conversion yield into N-acetylmannosamine, is known (patent document 1). In addition, a method of producing N-acetyl-D-mannosamine by reacting N-acetylneuraminate lyase with sialic acid as a substrate is also known (patent document 2). A method of controlling lectin binding to cell surface and a method of regulating nerve cell growth, by contacting acylated body of N-mannosamine with cells have been proposed (patent document 3). In patent document 3, N-acetyl-D-mannosamine is regarded as a negative control in promoting growth of axon in vitro.
The present inventors have found that N-acetyl-D-mannosamine is effective for improving brain hypofunction or improving sleep disorder (patent documents 4 and 5).